The present invention relates to a method for detecting a malfunctioning engine brake and a method for eliminating vibrations during engine braking with a malfunctioning engine brake.
An exhaust valve mechanism in an internal combustion engine, comprising at least one exhaust valve in each cylinder, a rocker arm shaft-mounted rocker arm for each cylinder for operating the exhaust valve, a cam shaft with a cam element for each rocker arm, said cam element cooperating with motion transmitting means at one end of the rocker arm, a first piston-cylinder device disposed between an opposite end of the rocker arm and the exhaust valve, said first piston-cylinder device having a first cylinder chamber in said opposite rocker arm end, a hydraulic circuit for supplying and draining off pressure fluid to and from said cylinder chamber, and a piston disposed in said cylinder chamber, said piston being biased towards the exhaust valve when pressure fluid is supplied to the cylinder chamber.
SE-A-468 132 describes an exhaust valve mechanism of the above mentioned type which, together with a special type of camshaft with exhaust cams with extra lobes can be used to increase the engine braking power. The extra cam lobes are dimensioned so that their lifting height corresponds to the normal valve play of the valve mechanism. By reducing, by means of the piston cylinder device, the valve plate to zero, one or more extra lifts of the exhaust valve corresponding to the normal valve play can be achieved during a suitable time interval. For example, an extra cam lobe can be placed in relation to the regular cam lobe so as to provide an extra exhaust valve lift during a later part of the compression stroke, resulting in a loss of a portion of the compression work during the compression stroke which will not be recovered during the expansion stroke. This increases the braking effect of the engine.
In an engine with such an arrangement, the maximum lift height of the exhaust valve during the compression when engine braking, is limited to the valve play. Furthermore, the overlap of the exhaust valve and the intake valve in braking mode increases by virtue of the fact that the maximum lift height of the exhaust valve increases by a distance corresponding to the valve play as compared to drive mode. Since the pressure in the exhaust manifold is much higher than the pressure in the intake manifold in braking mode (ca 5 bar on the exhaust side as opposed to ca 1 bar on the intake side), hot exhaust in an amount depending on the overlap will flow between the exhaust side and the intake side during braking mode, which will impair the engine cooling during braking mode as compared to driving mode, especially since fuel as a cooling medium for the injection nozzle is not available during braking mode. Finally, the exhaust rocker arm must be dimensioned more robustly for braking mode than for normal driving mode, since the opening force on the exhaust valve in braking mode must overcome the force from a high compression pressure in the cylinder, this force being substantially higher than the force on the valve required for normal opening during the exhaust stroke.
WO 03/002862 relates to a process and a control device of an engine comprising a barrier to decompression. The object of this invention is to increase the engine temperature as fast as possible. This is done by setting at least two cylinders in braking mode and at least two cylinders in non-braking mode (normal operation). The vibrations are kept at a minimum because at least two cylinders at a time are in the braking mode. Those cylinders are chosen in order to compensate for the other's vibrations
It is a need in the art for a method which can detect a malfunctioning engine brake and a method for reducing or eliminating engine vibrations caused by said malfunctioned engine brake.
It is desirable to provide a method for detecting and reducing vibrations caused by a malfunctioning engine braking.
According to a first aspect of the invention it is provided a method for reducing engine vibrations during engine braking with a malfunctioning engine brake, where said engine brake comprising means for altering a timing of at least one exhaust valve and means for varying an exhaust gas back pressure, comprising the steps of: detecting piston acceleration for each cylinder in the engine during the use of said engine brake, comparing said detected piston acceleration with a predetermined reference value, decreasing exhaust gas back pressure during engine braking if at least one piston is detected with a piston acceleration deviating more than a predefined amount from said predetermined reference value so that said piston acceleration will be falling within said predefined amount from said predetermined reference value.
An advantage of an aspect of the present invention is that it may minimize the effect of the potentially high valve forces created by the malfunctioning engine brake.
Another advantage of an aspect of the present invention is that malfunctioning cylinders are detected and possibly stored for later use/knowledge when servicing the engine.
In another example embodiment of an aspect of the present invention said reference value is another detected piston acceleration measured during engine braking.
An advantage of this embodiment is that no extra reference values need to be determined beforehand.
In another example embodiment of an aspect of the present invention said detected piston has the highest piston acceleration.
An advantage of this embodiment is that it always ensures that maximum available engine brake power is utilized without vibrations although one or a plurality of engine brakes may be defective.
In another example embodiment of an aspect of the present invention said exhaust gas back pressure is decreased by increasing the passage of exhaust gases in the exhaust system.
An advantage of this embodiment is that built in devices may be used for restoring the engine back to normal operation.
In another example embodiment said exhaust gas back pressure is decreased by opening guide vanes in a variable geometry turbo unit.
An advantage of this embodiment is that a regulation of increased or decreased back pressure can easily be performed.
In still another example embodiment of an aspect of the present invention said exhaust gas back pressure is decreased by decreasing the charging pressure provided by a turbo charger.
An advantage of this embodiment is that it may further minimize the effect of high valve forces.
According to a second aspect of the present invention it is provided a method for decreasing engine vibrations during engine braking with a malfunctioning engine brake, where said engine brake comprising means for altering a timing of at least one exhaust valve and means for varying an exhaust gas back pressure, comprising the steps of: detecting piston acceleration for each cylinder in the engine during the use of said engine brake, comparing said detected piston acceleration with a predetermined reference value, adjusting a valve play in a device for operating said exhaust valve during said engine braking if at least one piston is detected with a piston acceleration deviating more than a predefined amount from said predetermined reference value so that said piston acceleration will be falling within said predefined amount from said predetermined reference value.
In another example embodiment of an aspect of the present invention said device for operating said exhaust valve during engine braking is a hydraulic circuit and said adjustment is performed by altering a fluid pressure in said hydraulic circuit.
In still another example embodiment of an aspect of the present invention said device for operating said exhaust valve during engine braking is a mechanical slipping eccentric device which can be rotated in a suitable direction for achieving a correct exhaust valve play during engine braking which will cause a piston acceleration falling within said predefined amount from said predetermined reference value.
In still another example embodiment of an aspect of the present invention said device for operating said exhaust valve during engine braking is a mechanical slipping eccentric device which can be rotated in a suitable direction for achieving a correct exhaust valve play during engine braking which will cause a piston acceleration falling within said predefined amount from said predetermined reference value.
In still another example embodiment of an aspect of the present invention said reference value is another detected piston acceleration measured during engine braking.
In still another example embodiment of an aspect of the present invention said detected piston has the highest piston acceleration.
In still another example embodiment of an aspect of the present invention said exhaust gas back pressure is decreased by increasing the passage of exhaust gases in the exhaust system.
In still another example of an aspect of embodiment of the present invention said exhaust gas back pressure is decreased by opening guide vanes in a variable geometry turbo unit.
In still another example embodiment of the present invention said exhaust gas back pressure is decreased by decreasing the charging pressure provided by a turbo charger.
According to a third aspect of the present invention it is provided a method for detecting a malfunctioning engine brake, where said engine brake comprising means for altering a timing of at least one exhaust valve and means for varying an exhaust gas back pressure, comprising the steps of: detecting piston acceleration for each cylinder in the engine during and/or after the use of said engine brake, comparing said detected piston acceleration with a predetermined reference value, alerting during and/or after the engine braking if at least one piston is detected with a piston acceleration deviating more than a predefined amount from said predetermined reference value.
In still another example embodiment of an aspect of the present invention said alerting comprises the step of sending a signal to an ECU (Electronic Control. Unit) that one or a plurality of engine brakes are malfunctioning and/or sending a signal to the driver while driving a vehicle having an engine with said malfunctioning engine brake.